1. Field of the Invention
This invention relates to the field of integrated circuit technology, and in particular to contact springs for use in an integrated circuit test probe.
2. Description of Related Art
EP 0755071 discloses a test device that comprises an integrated circuit (hereinafter a xe2x80x9cprobe ICxe2x80x9d) with protruding xe2x80x9csolder bumpsxe2x80x9d that are designed to contact pads on a corresponding integrated circuit that is to be tested (hereinafter a xe2x80x9cDUTxe2x80x9d, Device Under Test), and is incorporated by reference herein. The probe IC preferably contains circuitry to facilitate the testing of the DUT, and the bumps provide the communication of power and test signals and corresponding responses, to and from the DUT. The bumps are fabricated on the probe IC to correspond to the location of test points on the DUT. Because multiple test points must be contacted simultaneously, the protrusion of each bump must be substantially equal, to form a uniform contact plane.
An alternative to the use of solder-bumps is the use of pre-formed balls that are mounted to the planar surface of the probe IC, as illustrated in FIG. 1. Uniformly sized balls 130 are mounted on a probe IC 120, which is mounted on a test device substrate 110. Connections 115 provide communication between the probe IC 120 and other test equipment (not shown), via circuitry on the substrate 110. If the balls 130 are of uniform size, a uniform contact plane is provided, as illustrated in FIG. 1 by the dashed line 101. When the balls 130 are brought in contact with pads 140 on a DUT 150, via a movement 190 of the test structure that includes the probe IC 120 toward the DUT 150, or a movement of the DUT 150 toward the probe IC 120, contact is established, and testing may be performed by communicating test stimuli and responses to and from the DUT 150. The use of uniform sized balls, however, limits the pitch, or test-pad-density, that can be achieved.
FIG. 2 illustrates another alternative to the solder-bump or uniform-ball contact techniques, wherein spring levers 230 on the probe IC 120 are used to contact the pads 140 of the DUT 150. Using thin-film microspring technology, a pitch as dense as 6 micrometers can be achieved, compared to an approximate 400 micrometer limit to the aforementioned uniform-ball contact technique. The cost and complexity of fabricating microsprings, however, limits the application of this technique for widespread use. Additionally, the extent of the spring element 230 below the probe IC 120 using microspring technology is limited, and may not provide sufficient clearance between the components of the test structure, such as the connectors 115 between the probe IC 120 and the substrate 110, and the DUT 120.
An alternative to the use of microsprings is the use of bonding wire that is treated to be resilient. xe2x80x9cTHE FINAL TEST REPORTxe2x80x9d, Vol. 12, No. 9, Sep. 2001, introduces such a technique developed by FormFactor, Inc. of Livermore, Calif. In this approach, the bonding wire 330 is attached to a bond pad at one end, and formed into an xe2x80x9cSxe2x80x9d shape to provide a resilient spring, as illustrated in FIG. 3. The resilient spring shape provides tolerance for a non-uniform contact plane, and can be formed to a length that sufficiently clears the connectors 115. Consistently forming an S shape with a free-standing bonding wire, however, is a non-standard use of a bonding wire machine, and requires a two-step process. To form the S shape, the bonding wire must be non-resilient; to provide the required resiliency, the resilient coating must be subsequently applied. As multiple springs are formed, maintaining the required shape in the non-resilient bonding wire may be problematic, and the subsequent application of the resilient coating to a field of S shaped bonding wire springs is also likely to be problematic.
It is an object of this invention to provide a method and system that facilitates contact between two integrated circuit devices. It is a further object of this invention to provide a method and system that facilitates the testing of an integrated circuit. It is a further object of this invention to provide a method and system that facilitates contact between two integrated circuits that uses conventional manufacturing processes.
These objects and others are achieved by providing a method and system wherein bonding wire is formed into an inverted xe2x80x9cVxe2x80x9d shape by bonding both ends of a bonding wire to adjacent points on an integrated circuit. One end of the bonding wire is bonded to a specified point on the integrated circuit, the bonding head is raised, and then lowered to an immediately adjacent point to effect the second bonding, thus forming the inverted V shape. This V shape, being bonded at both ends, is mechanically stable, is resilient in form, and allows for the use of resilient, or non-resilient bonding wire. The vertex of the V shape forms a point or surface for contacting another integrated circuit, or other device, for communicating signals to and from the device to which the bonding wire is bonded.